package com.kevin.redisson.configuration;

import lombok.extern.slf4j.Slf4j;

@Slf4j
public class Snowflake {

    /**
     * 起始的时间戳
     */
    private final static long START_TMP = 1480166465631L;

    /**
     * 每一部分占用的位数
     */
    private final static long SEQUENCE_BIT = 12;  // 序列号占用的位数
    private final static long MACHINE_BIT = 5;    // 机器标识占用的位数
    private final static long DATACENTER_BIT = 5; // 数据服务占用的位数

    /**
     * 每一部分的最大值
     */
    private final static long MAX_DATACENTER_NUM = ~(-1L << DATACENTER_BIT);
    private final static long MAX_MACHINE_NUM = ~(-1L << MACHINE_BIT);
    private final static long MAX_SEQUENCE = ~(-1L << SEQUENCE_BIT);

    /**
     * 每一部分向左的位移
     */
    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTAMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

    private final long datacenterId;  // 数据服务
    private final long machineId;     // 机器标识
    private long sequence = 0L;       // 序列号
    private long lastTmp = -1L;       // 上一次时间戳

    public Snowflake(long datacenterId, long machineId) {
        log.info("------------nodeId:{},machineId:{}------------", datacenterId, machineId);
        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
            throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
        }
        this.datacenterId = datacenterId;
        this.machineId = machineId;
    }

    /**
     * 产生下一个ID
     */
    public synchronized long nextId() {
        long currStmp = getNewTimestamp();
        if (currStmp < lastTmp) {
            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
        }

        if (currStmp == lastTmp) {
            // 相同毫秒内，序列号自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            // 同一毫秒的序列数已经达到最大
            if (sequence == 0L) {
                currStmp = getNextMill();
            }
        } else {
            // 不同毫秒内，序列号置为0
            sequence = 0L;
        }

        lastTmp = currStmp;

        return (currStmp - START_TMP) << TIMESTAMP_LEFT  // 时间戳
                | datacenterId << DATACENTER_LEFT        // 数据服务
                | machineId << MACHINE_LEFT              // 机器标识
                | sequence;                              // 序列号
    }

    private long getNextMill() {
        long mill = getNewTimestamp();
        while (mill <= lastTmp) {
            mill = getNewTimestamp();
        }
        return mill;
    }

    private long getNewTimestamp() {
        return System.currentTimeMillis();
    }

}
